1. Field of the Invention
The present invention relates to a tone and voice shared remote control system for radio communications and more particularly to an automatic gain control circuit for use in a symmetrical signaling circuit in each unit of the remote control system for controlling the operation of one or more additional units of the system, all of which are coupled to a single audio channel.
2. Description of the Prior Art
Heretofore, various remote control systems for enabling a remote console to control a base station coupled to a transmitter and receiver have been proposed. Examples of several of these systems are disclosed in the following U.S. patents:
______________________________________ U.S. PAT. NO. PATENTEE ______________________________________ 3,577,080 Cannalte 4,184,118 Cannalte et al 4,208,631 Beseke et al ______________________________________
The system for remote control of a base station disclosed in U.S. Pat. No. 3,577,080 utilizes tone controls which are supplied over wire lines. A variety of different tone controls can be generated and transmitted over the wire lines to control various functions of the base station. This system is limited by the fact that signaling is initiated strictly from the remote control console (point of control) for commanding the execution of functions at the base station.
The base station feedback reporting system disclosed in U.S. Pat. No. 4,184,118 is an improvement over the previous remote control system and includes a tone control system that allows for acknowledgement from the base station of the function command received from the remote console. In this way system reliability is improved by indicating functional line interconnection and communication by the remote console with the base station.
U.S. Pat. No. 4,208,631 discloses a digital pulsed DC remote control system. This system utilizes digital pulsed DC signaling to select a radio channel of a base station transmitter for transmission of a message and does not utilize tones as does the system of the present invention.
There has also been proposed in U.S. Pat. No. 4,209,131 a computer-controlled irrigation system where remote sensors and fluid delivery systems are controlled by a central control station having a computer and interface circuits.
In the systems disclosed in the patents referred to above, the number of tone command functions is greatly limited. Furthermore, function commands are restricted to tone transmission from the control point to the base station and not vice versa.
Still further, the protocol in these prior systems for data transfer is not expandable and incapable of transferring great amounts of data information between the remote consoles and base stations.
Moreover, in the systems disclosed in the Cannalte patents, the signaling times are fixed. In particular, the windows for function tones can be opened for fixed periods of time to receive one or more function tones. This situation fosters low reliability due to falsing from noise signals or voice signals. Additionally, there exists no method in these prior systems for a remote console to determine the latched state of a base station without initiating a function change to a given known state.
Furthermore, in these prior systems there is no mechanism for a base station to initiate an unsolicited data transmission or an interrupt alarm signal or a status signal to a remote console.
Also, in the prior systems, multiple remote consoles and multiple base stations cannot be accomodated or coupled to a common audio channel or wire line while still maintaining uniform positive system integrity, knowledge of system state by all remote consoles and base stations and inherent muting of data sequences on parallel control positions.
As will be described in greater detail hereinafter, the remote control system having voice shared, tone, symmetrical, signaling circuits for radio communications of the present invention differs from the previously proposed systems by including one or more remote consoles and/or one or more base stations coupled to a single common wire line/audio channel. Each base station and remote console having a symmetrical signaling circuit with a plurality of modes of operation that provide inherent self-diagnostic capability and potential interface to external sources of digital data.
Moreover, in the systems of the present invention, gated sequential tone signaling is time multiplexed and compatible with the audio information to be transferred between units, whether they be base stations and/or remote consoles.
In addition, priority or preference in initiation of signaling over the audio channel or wire line is possible by any remote console or base station. All other units of base stations or remote consoles are responsive to this initiation of signaling in a well defined and predetermined manner by the alteration of internal status states within the control unit of each signaling circuit and possibly by the participating in the data exchange by acknowledge or reply from a receiving signaling circuit.
Still further, the signaling protocol utilized is highly structured to permit a high degree of flexibility and expansion in data interchanges while necessitating minimum degradation in basic system performance such as by the introduction of any delay or interference of normal voice transmission.